Dvd Decrypter slow write.

I use my dvd decrypter to back up my orginal movie, reading seem fine...but when i try to write it...it only write at 2X MAX, my dvd-media is 4X, my burner can write at 4X as well, i did set the Write Rate to Max BUT still i only able to write at 2X Max.
BTW if i use Nero it will burn 4X, just dvd decrypter not able to burn at 4X!!!!
Can someone help pls thanks